The maxillary sinus has a significant effect on diagnosis and semiology among craniofacial structures. Technological advances and the development of systems for the three-dimensional representation of this structure permit us to evaluate, through CBCT, specific alterations or sinus pathology. To date only few articles have been publish in literature assessing the relationship between frontal sinus and various cephalometric features using three-dimensional imaging. Gursoy et al. performed a recent research investigating the three-dimensional morphology of the frontal sinus in relation to the vertical dimension, but they assessed only linear measurement without calculating the volume and surface of the sinus [27].
Thus, the present study has investigated the correlation between the volume, surface, and maximum depth, height and width of the frontal sinuses and the facial growth pattern. The sample has been categorized by age because the physiological dimensional changes of the frontal sinus after 12 years of age are minimal and the sinuses growth rate after the growth peak slows down. For this reason, patients at the end of their pubertal growth spurt were considered.
The results of the 3D evaluation showed that volume, surface, and depth of the frontal sinus are on average greater in men than in women with statistically significance, confirming the results of a similar previous study [34].
The increasing of the volume, the surface, and the three dimensions of the frontal sinus recorded was correlated with the increasing of the age of the subjects with no statistically significance.
These two associations have already been investigated with smaller samples, on cephalograms in postero-anterior projects, therefore the bidimensional measurements were not realistic [35, 36].
In a retrospective study conducted on 32 skulls, the paranasal sinuses evaluation by CBCT showed that the depth and the volume of the frontal sinus increased with age (p <0.05) [37]. The sample of this study was divided into three age groups with a much greater variability (from 21 to 80 years) compared to ours.
Buyuk et al. [35] investigated the association between the frontal sinus morphology and the sex of 148 Turkish young adult subjects. The measurements were performed on bidimensional postero-anterior cephalograms and the authors found that the frontal sinus were larger in males than in females as demonstrated in our study. Moreover, the aforementioned study affirmed that frontal sinuses were unique due to their morphological characteristics to each individual, and in the field of forensic science, these features were very significant for personal identification.
In a further study, which aimed to investigate whether there was a relationship between skeletal maturation and frontal sinus morphology, through measurements made on postero-anterior projection teleradiographs of 220 growing subjects (aged between 8 and 18 years), a statistically significant difference was found between the width of the frontal sinus in men and women, in favor of the former [36]. These results agree with those obtained by the authors of the present study. The authors subsequently investigated the possible relationship between frontal sinus size and facial morphometric and bio typological characteristics.
Previous investigations have pointed out a relation between frontal sinus characteristics and the craniofacial growth pattern [9, 38].
A research made by Rossouw et al. [9] showed that there was a significant correlation between the area of the frontal sinus, calculated on bidimensional latero-cephalograms, and the maxillary and mandibular length, symphysis dimension, and condylar length, assuming that the increase in volume of the frontal sinuses can be considered as an additional predictor for mandibular growth. In our research, the correlations related to the skeletal class, the position of the maxilla and mandible with respect to the base were investigated. The univariate regression models corroborate the results of the previous study, in fact it found a statistically significant interaction between the SNB angle, that represent the dimension of the mandibular bone, and the volume, surface, width and height of the frontal sinus.
However, the results present in literature are in contrast. Dah-Jouonzo et al. [38] assessed the relation between the frontal sinuses volume and the maxilla-mandibular relationship in 95 subjects and evinced that the volume of the sinus is mainly affected by the changes in vertical dimensional than in the sagittal one. The research observed also that the average sinuses volume was larger in patients presenting class III malocclusion, followed by class II division 1, whereas subjects with class II division 2 malocclusion and class I were comparable [38]. This study took into consideration a sample like ours in terms of number and in this case the measurements were carried out on CBCT scans. In fact, the results partially match ours, since also in this study the relationship between the anterior vertical skeletal dimension and the volume of the frontal sinuses is evident. In this case, however, the sample was not divided into age groups and by sex.
Other authors in a 2017 study involving 144 subjects hypothesized that the frontal sinus pneumatization pattern would affect the skeletal growth pattern and could be used as a growth predictor [39]. Skull teleradiographs in postero-anterior and latero-lateral projection were used to measure the size of the frontal sinus. The results of this study showed an association between an increased size of the frontal sinus and a reduced inclination of the anterior skull base. In males, larger frontal sinus sizes were associated with increased anterior vertical dimension; in females, on the other hand, to an increase in the gonial angle [39].
A study published by Said et al. [40], examining the postero-anterior and lateral cephalograms of 1226 patients, demonstrated the correlation between cephalometric parameters such as the anterior skull base, the facial height, the inclination of the upper incisors and the size of the frontal sinus. Since these assumptions, the authors were able to affirm that the volume of the frontal sinus could be used as an indicator of a correct and harmonious anterior occlusion (22). The sample in this case is extremely large, however the limit of this study consists in the having carried out the measurements on two-dimensional radiographic examinations that are not able to return real measurements of the anatomical structures, but perspective. The results obtained are however in line with those of the current study.
A more recent investigations performed on lateral cephalograms by Yassaei et al. [41] demonstrated that paranasal sinus such (frontal and maxillary sinus) were bigger in patients presenting class III malocclusion than those presenting class 1 and class 2. Moreover, the authors showed a statistically significant positive correlation between the frontal sinus width and the dimension of the anterior cranial base. In contrast to the results of the present study, the previous study reported no statistically significant correlation has been found between the indexes of the skeletal vertical dimensions and the frontal sinus dimensions [41]. The reason behind this difference in results can be attributed to the use of lateral cephalometric radiographs. Overlap of the right and left frontal sinus on lateral cephalograms produce an inaccurate identification of the anatomical structures. In the present study, the three-dimensional frontal sinus measurements (volume, surface, height, width, and depth) were computed on the sagittal axial, and coronal sections of the CBCT scans, each sinus has been isolated and reconstructed with a 3D rendering which enabled more accurate measurements.
The diffusion of the CT cone beam in the dental field has allowed the volumetric study of the anatomical structures with high reliability. This study will allow us to have a clearer view of the mechanisms that regulate function and growth.
As previously demonstrated craniofacial alterations could frequently be related to the airway problems, so the necessity of assessing the correlation between frontal sinus morphologies and craniofacial features may be relevant. In 1993 Wolf et al. [42] reported that paranasal sinus growth was correlated with cranio-facial and dental growth. In this case our findings could provide an understanding of a possible relationship between frontal sinus development and facial growth.
Based on the present results, it can be said that young adults in whom the frontal sinuses have reached their maximum size (while vertical growth continues) a larger frontal sinus may be associated with future vertical growth. Longitudinal studies are required to state that the frontal sinuses can be considered as predictors of growth.